IN the wake of the NSA surveillance scandal, Barack Obama's credibility is under scrutiny like never before.

Whether using drones for the 'targeted killing' of alleged terrorists or data-mining the phone records of everyone in America, he has a standard response to those who question his use of these questionable clandestine programmes: "We welcome a debate."

That debate has exploded into the open following this week's revelations about the extent of National Security Agency surveillance programmes.

Mr Obama's offer of debate sounds all very liberal and reasonable but for his frustrated critics on both the liberal Left and libertarian Right the offer is nothing more than a cover for a president who campaigned as a liberal but on national security has governed as an outright authoritarian.

If Mr Obama really wanted a debate on drones, or the ethics of dragnet-surveillance of the phone records of all Americans, they ask, why has it taken a series of damaging leaks for his administration to even admit the existence of these programmes, let alone openly debate them?

In this debate, Mr Obama relies almost entirely on his 'credibility'. Ultimately the US public will be the judge of his credibility and he seems – perhaps rightly – pretty confident of their support.

Just three months ago, Senator Ron Wyden, a Senate Intelligence Committee member, asked James Clapper, the Director of National of National Intelligence: "Does the NSA collect any type of data at all on millions or hundreds of millions of Americans?"

"No sir," came Mr Clapper's reply – which, as we now know, was a flat-out lie.